Speed is the rate at which something moves. Fast-moving objects have high speeds, slow-moving ones have low speeds, and objects with no movement have zero speed. Velocity, on the other hand, is speed in a particular direction. Velocity is what's called a vector quantity, which is any quantity -- velocity, force, acceleration, torque -- that has both magnitude and direction. Racecar teams are most interested in improving average speed around a track. Because all cars can move quickly along the straight sections of a track, racecar designers modify a car so that it performs best especially when cornering.

Designers take into account the forces that act upon the car as it moves around the track. Downforce keeps a car stuck to the road by increasing friction and stability, while drag is the air resistance that slows a car. Maximizing downforce and minimizing drag are the primary goals of most design modifications. An airplane wing is shaped so that air pressure under the wing is greater than that above the wing, and lift force is generated. Attaching wings upside-down to the front and rear of a racecar, then, is one way to generate additional downforce. Increasing downforce inevitably results in increased drag, however. Because drag is proportional to the square of the speed a car is moving, drag reduction is crucial. So just as aeronautical engineers design airplane wings to maximize lift-to-drag ratios, racecar designers seek to modify wing attachments to maximize downforce-to-drag ratios.

According to Newton's law of inertia, an object already in motion will continue to move in a straight line at a constant speed unless acted on by an outside force. Centripetal force is the force that pushes or pulls a car inward so that it moves around the corners. For this force to be applied to the tires by the road, sufficient friction must be generated by tires pushing down on its surface. Race teams make adjustments to front or rear wings to alter the grip of the tires and improve overall balance.

Design helicopters that fall as slowly as possible in this NOVA classroom activity.